Best thing you can do is get a tree surgeon to cut it down in pieces
and then poison the whole root system. It will die off fairly quickly
once it's been poisoned.
You will not be able to partially kill the roots near your pipes,
they'll just keep coming back. Poplars are well-known for damaging
water pipes, so it your already worried about it get it felled.
Don't wait another 5 years so it's grown another 20 feet, it'll cost
you more to remove it then.
Bill, Edinburgh